Breast cancer is cancer that frequently occurs in women, and many techniques for the accurate diagnosis and treatment of breast cancer are being developed. Typical methods for the treatment of cancer such as breast cancer and the like include surgery, radiation therapy, and chemotherapy. Among them, chemotherapy is useful in the treatment of cancer by disrupting the replication or metabolism of cancer cells, but is disadvantageous in that it kills not only cancer cells but also normal cells. In order to solve this problem, widely useful is a targeted therapy for the treatment of cancer by targeting a specific protein (e.g. HER2 (Human epidermal growth factor receptor 2), which is overexpressed in breast cancer, or the like) that is expressed in the cancer, as disclosed below.